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Thread: How to use the MOSFET Power Board

  1. #11
    Constant Bitrate ACCLR8N's Avatar
    Join Date
    Apr 2009
    Davisburg, MI
    "It's like he's trying to speak to me, I know it. Look, you're really cute, but I can't understand what you're saying. Say the first thing again." -Marlin, Finding Nemo

  2. #12
    Raw Wave
    Join Date
    Nov 2009
    The first bit is simple. It's not fire, it's fatal.
    The danger is not smoke and flames, but the death of someone.
    (Connect the FB to an AC supply and if somebody dies.... I don't think I need say more. But now that I have, FB have little choice....)

    The second part explains methods of dimming AC circuits. Simple & ancient. Used for tungstens, fluoros, motors etc.
    Seek and ye shall find.

  3. #13
    Low Bitrate UniqelyCommon's Avatar
    Join Date
    Nov 2008
    Teh Internets
    Quote Originally Posted by OldSpark View Post
    The same opto-TRIAC (or two SCRs) circuit is used for phase control which is PWM (where "on" occurs after a phase delay and stays on until next zero crossing)
    Oh, I was thinking of controlled by PWM, my bad. Heh, helps to ask the right question, eh?

  4. #14
    Raw Wave
    Join Date
    Nov 2009
    Well you'd use the same opto or equivalent for PWMing of AC...

    But since once triggered, SCRs/TRIACs are ON until zero current (ie, zero crossing), it's not like you can turn them off as with PWM. FETs, IGBTs, transistors etc - yes, cool for PWM.

    But SCR/TRIAC "phase control" is like PWM.
    VIZ: A self regulating PWM circuit - eg, and SMPS. If the PWM triggered SCRs instead of FETs, the output voltage would swing higher than desired, hence the next trigger would be delayed to compensate.
    That might not be a problem if hi-frequency, but SCRs etc are usually only suitable a few kHz (I think).

    But as I wrote, despite PWM similarities, it's easier NOT using the Brain's or PIC's PWM output for such circuits.

    I may have confused readers that weren't aware of the three distinct things I was discussing - using any output to control a 110-240VAC device (isolation is required); using an opto-coupler to isolate and control anything (SCR; MOSFET); using PWM to vary output... an SCR-controlled lamp is a form of PWM (look at its current) despite its controller emitting fixed-width pulses - ie, phase control where ON = phase (a short pulse from the controller) and OFF is the next zero-crossing.

    But I did want to highlight that sometimes a dimmer etc does not require the PWM output....

  5. #15
    Variable Bitrate
    Join Date
    Sep 2007
    Export, PA
    question nick...

    would i be able to use this in conjunction with my car's PCM to drive a Coil On Plug setup, using the PCM's ignition triggers to trigger the power board? car uses constant +12v, 2 switched grounds, which is exactly what your power board handles...

    lemme know, if you jump on msn anytime soon that would be cool too...
    Planning: [|||||||||-] 90%
    Purchased: [|||||||||/] 99%
    Installation: [|||||||||-] 90% (when is anyone's project ever REALLY done...)

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